Search results for "Crystallization"
showing 10 items of 774 documents
Upconversion luminescence of Er3 +/Yb3 + and their role in the stabilization of cubic NaLaF4 nanocrystals in transparent oxyfluoride glass ceramics
2018
CC BY-NC-ND
Preparation and characterization of continuous fly ash derived glass fibers with improved tensile strength
2018
Abstract The coal-based energy production in China generates more than 600 million tons of coal fly ash (CFA) each year, which drives us searching for new methods for recycling CFA. In this work, continuous glass fibers with a range of CFA (25–45%) were successfully prepared without showing any sign of fiber crystallization. The measured fiber tensile strength was found to increase with CFA proportionally. The fiber derived from 45% CFA exhibited the best tensile strength (higher than the E glass fiber prepared/tested under the same conditions) and good chemical stability (98% mass retention in the acid corrosion test). Our study shows a feasibility of making continuous CFA derived glass fi…
Mechanism of crystallization of pyroxene-based glass-ceramic glazes
2004
Abstract The mechanism of crystallization of a powdered glass with composition in the pyroxene crystallization primary field within the CaO–MgO–Al 2 O 3 –SiO 2 quaternary system and containing some additives was studied. The crystallization sequence was compared with that from the same base glass without additives. After a short thermal anneal both powdered glasses showed phase separation. Further thermal treatment gave rise to the crystallization of pyroxene. Anorthite as secondary crystalline phase was also detected in the quaternary glass (without additives). The starting crystallization in the glass with additives took place in the outer surface of glass particles probably in the immisc…
Li2OSiO2Al2O3MeIIO Glass-Ceramic Systems for Tile Glaze Applications
1991
In order to verify the possibility of using glass-ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li2O─Al2O3─SiO2 glass-ceramic system were investigated by differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, devel…
Microstructural Evolution in Fast-Heated Cordierite-Based Glass-Ceramic Glazes for Ceramic Tile
2004
The crystallization mechanism of α-cordierite from a B 2 O 3 -and TiO 2 -containing glass submitted to fast heating in the cordierite primary phase field of the CaO-MgO-Al 2 O 3 -SiO 2 quaternary system was investigated. Addition of B 2 O 3 to a SiO 2 -rich glass suppressed the formation of μ-cordierite. This suppression facilitated densification by viscous flow before crystallization. Powder X-ray diffractometry, field-emission electron scanning microscopy, and energy-dispersive X-ray analysis revealed that α-cordierite nucleated directly from glass on the boundaries of original particles and was probably favored by TiO 2 , which acted as a nucleant. The growth kinetics of α-cordierite cry…
Thermoelectric properties of p-type Bi2Sr2Co2O9 glass-ceramics
2014
In the oxide system of Bi–Sr–Co glass melts have been prepared by adding a small amount of glass formers. A crystallization leads to crystalline phases of Bi8Sr8Co4O25, BiSrCo2Ox and Bi2Sr2Co2O9 (BC-222) densely embedded into a residual glass phase. This work shows the possibility of obtaining microstructured bulk material with low thermal conductivity and relatively high electrical conductivity via such a glass ceramic approach. Furthermore the stability of these materials under thermal cycling for temperatures up to 700 °C is shown. A characterization of the thermoelectric properties leads to a figure of merit (ZT) between 0.008 and 0.018.
Highly Robust but Surface-Active: N-Heterocyclic Carbene-Stabilized Au25 Nanocluster as a Homogeneous Catalyst
2019
<div> <div> <div> <p>Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface-active for liquid-phase catalysis without any pre-treatment. Herein, we report a novel N-heterocyclic carbine-stabilized Au25 nanocluster with high thermal and air stabilities as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au25(iPr2-bimy)10Br7]2+ (iPr2-bimy=diisopropyl-benzilidazolium) (1), was synthesized by direct reduction of AuSMe2Cl and iPr2- bimyAuBr with NaBH4 in o…
A neutron tomography study: Probing the spontaneous crystallization of randomly packed granular assemblies
2018
We study the spontaneous crystallization of an assembly of highly monodisperse steel spheres under shaking, as it evolves from localized icosahedral ordering towards a packing reaching crystalline ordering. Towards this end, real space neutron tomography measurements on the granular assembly are carried out, as it is systematically subjected to a variation of frequency and amplitude. As expected, we see a presence of localized icosahedral ordering in the disordered initial state (packing fraction around 0.62). As the frequency is increased for both the shaking amplitudes (0.2 and 0.6 mm) studied here, there is a rise in packing fraction, accompanied by an evolution to crystallinity. The ext…
Rapid nanocrystallization of soft-magnetic amorphous alloys using microwave induction heating
2009
The crystallization of Fe73Nb3Cu1Si16B7 alloy during microwave heating was investigated in situ using synchrotron radiation powder diffraction. The phase transformation comprises a primary nanocrystallization stage and a final microcrystallization step. We provide evidence for a strong enhancement of the transformation kinetics. Microwave heating occurs as a result of both ohmic and magnetic losses induced by eddy currents, which defines a volumetric microwave induction heating process. Nanocrystallization is completed within 5 s, while full crystallization is achieved in less than 10 s.
Spatially resolved nanostructural transformation in graphite under femtosecond laser irradiation
2015
Abstract A polycrystalline graphite target was irradiated using infrared (800 nm) femtosecond (120 fs) laser pulses of different energies. Increase of sp 3 bonds percentage and possible diamond crystal formation were investigated ‘in-depth’ and on the irradiated surfaces. Synchrotron X-ray diffraction pattern have shown the presence of a diamond peak in one of the irradiated zones while X-ray photoelectron spectroscopy investigations have shown an increasing tendency of the sp 3 percent in the low power irradiated areas and similarly ‘in the depth’ of the higher power irradiated zones. Multiple wavelength Micro-Raman investigations have confirmed this trend along with an ‘in-depth’ (but not…